1. Field of the Invention
This invention relates to a heat conductive silicone composition and a heat conductive silicone article obtained by shaping the composition into a sheet. The heat conductive silicone article is effective as a heat transfer medium interposed between a thermal boundary face of a heat generating electronic part and a heat sink or a heat dissipating member as in a circuit board for the purpose of cooling the electronic part.
2. Background Art
Now that CPUs, driver ICs, memories and other LSI chips used in electronic equipment such as personal computers, digital versatile disks, and mobile phones have made great progress toward higher performance, higher operating speed, size reduction and higher integration, they generate large amounts of heat by themselves. A temperature ramp of a chip by such heat causes malfunction and even failure to the chip. Thus, a number of heat dissipating techniques and heat dissipating members used therefor have been proposed for restraining the chip from a temperature rise during operation.
In prior art electronic equipment, a heat sink in the form of a plate of aluminum, copper or similar metal having a high heat conductivity is used for restraining the chip from a temperature rise during operation. The heat sink functions to conduct the heat generated by the chip and release the heat from its surface by utilizing the temperature difference between the heat sink and the ambient air.
For efficient transfer of the heat generated by the chip to the heat sink, the heat sink must be placed in close contact with the chip. Because of difference in chip dimensions and tolerances associated with assemblage, a flexible sheet or grease is often interposed between the chip and the heat sink so that heat transfer takes place from the chip to the heat sink via the sheet or grease.
Since sheets are easy to handle as compared with grease, heat conductive sheets made of heat conductive silicone rubber or the like (typically heat conductive silicone rubber sheets) are used in a variety of applications.
For these heat conductive sheets, a strong stress is often applied to compress the sheet in order to improve its contact with the chip and the heat sink. In the case of an elastomer sheet, residual stresses can adversely affect the chip. JP-A 2002-33427 discloses a heat dissipating sheet prepared by applying an organohydrogensiloxane to a film, sandwiching an unvulcanized compound between a pair of coated films, and heat molding the assembly, thereby producing a heat dissipating sheet comprising thin film reinforcing layers of cured rubber as upper and lower surface layers and an unvulcanized compound layer therebetween. However, the step of applying organohydrogensiloxane to upper and lower films is added to the molding process, which becomes disadvantageous for mass-scale manufacture.